초록 ▼

A semi-submersible, multicolumn, deep draft, floating offshore oil and gas drilling and production platform comprises a floating hull having an adjustably buoyant base, a plurality of columns vertically upstanding from the base, and an equipment deck that is supported atop the columns when the platf

A semi-submersible, multicolumn, deep draft, floating offshore oil and gas drilling and production platform comprises a floating hull having an adjustably buoyant base, a plurality of columns vertically upstanding from the base, and an equipment deck that is supported atop the columns when the platform is operationally deployed. Each of the columns comprises a cellular structure that includes a plurality of elongated tubes having a variety of cross-sectional shapes extending from the base to the top of the column. Each of the tubes defines one or more closed compartments. At least one of the compartments has a buoyancy that is fixed, and at least another one of the compartments has a buoyancy that is adjustable. The buoyancy of the compartments and the base can be controllably adjusted with pressurized air to provide a safer and less costly method for deploying the platform for offshore operations.

대표청구항 ▼

1. A hull for an offshore semi-submersible platform, comprising:a base having an adjustable buoyancy; and, a plurality of upstanding columns connected to the base, each column comprising a plurality of elongated, closely-spaced cylindrical tubes connected together by a plurality of vertically elonga

1. A hull for an offshore semi-submersible platform, comprising:a base having an adjustable buoyancy; and, a plurality of upstanding columns connected to the base, each column comprising a plurality of elongated, closely-spaced cylindrical tubes connected together by a plurality of vertically elongated webs to form a plurality of non-cylindrical interstitial tubes interspersed with the cylindrical tubes, each of the cylindrical tubes defining a plurality of vertically-arranged, substantially cylindrical compartments, and each of the interstitial tubes defining a plurality of vertically-arranged, non-cylindrical interstitial compartments; wherein at least one of the cylindrical compartments has a buoyancy that is fixed and at least one of the interstitial compartments has a buoyancy that is adjustable. 2. The hull of claim 1, wherein at least one of the webs is substantially planar.3. The hull of claim 1, wherein at least one of the webs is arcuate.4. The hull of claim 1, further comprising a horizontal bulkhead subdividing the cylindrical and interstitial tubes into cylindrical and interstitial compartments, respectively.5. The hull of claim 1, wherein the at least one adjustably buoyant compartment comprises:an opening to ambient sea water at a lower end of the compartment; means for introducing pressurized air into an upper end of the compartment; and, means for venting the upper end of the compartment to atmospheric pressure. 6. The hull of claim 1, wherein at least one of the cylindrical tubes comprises a shaft providing access to at least some of the compartments.7. A method for deploying a floating deep-draft semi-submersible offshore platform, comprising:providing a hull having an adjustably buoyant base and a plurality of upstanding, adjustably buoyant columns at an inshore water site; de-ballasting the hull to a shallow draft configuration; towing the hull in the shallow draft configuration to an intermediate site having deeper water that is shielded from wind and waves; ballasting the hull such that top ends of the columns extend slightly above the surface of the water; providing a deck supported by a buoyant deck barge; transferring the weight of the deck from the barge to the top ends of the columns; securing the deck to the columns to form the semi-submersible platform; de-ballasting the hull to an intermediate draft configuration; towing the platform to an operation site in the intermediate draft configuration; ballasting the hull to an operational draft configuration; and, anchoring the platform at the operational site with a mooring system. 8. The method of claim 7, wherein transferring the weight of the deck from the barge to the top ends of the columns comprises:floating the barge between the columns such that the deck is disposed over the top ends of the columns; and, de-ballasting the columns such that the deck is lifted off the barge by the columns. 9. The method of claim 7, wherein transferring the weight of the deck from the barge to the top ends of the columns comprises:floating the barge between the columns such that the deck is disposed over the top ends of the columns; and, ballasting the barge down such that the deck is lifted off the barge by the columns. 10. The method of claim 7, wherein ballasting the hull comprises:selecting a first set of ballast tanks in the base of the hull to be completely flooded with sea water ballast; selecting a second set of ballast tanks in the base to be partially filled with sea water ballast; pressurizing air in the second set of tanks to a pressure that is about the same as the hydrostatic pressure of the sea water at a depth equal to the height of the columns of the hull; opening the first set of tanks to ambient sea water such that all air in the tanks is completely displaced with sea water; opening the bottoms of the second set of tanks to ambient sea water; and, venting the top of the second set of tanks to the atmosphere in a controlled manner. 11. The method of claim 7, wherein the columns comprise adjustably buoyant compartments, and wherein de-ballasting the hull comprises connecting pressurized air in lower ones of the compartments to higher ones of the compartments.